#!/usr/bin/env python3
#coding:utf-8

import math
from sys import stdin
# import numpy as np
# from matplotlib import pyplot as plt



def main():
	read=stdin.readline

	#edit here!
	k=int(input())
	dp=[0]*(k+10)

	for i in range(k):
		dp[i]+=1.0
		for j in range(6):
			dp[i+j+1]+=dp[i]/6

	print(dp[k-1])
if __name__ == '__main__':
    main()